An electronic transmission-shifting control implemented with digital logic is known in which a shifting process is conducted substantially in dependence upon the output RPM and a torque stage of the transmission (German patent document-Auslegeschrift No. 2,338,122).
Actual acceleration values are determined from the output RPM. These are compared for each speed ratio with stored acceleration values. Upshifting and downshifting are effected in dependence upon the output RPM (i.e. the rotation rate of a transmission output shaft) which is compared with stored speed-ratio-dependent, torque-dependent and acceleration-dependent RPM limits. The upshifting is effected, for example, in the torque stage of full gas or kick-down and reduced acceleration values, corresponding to reduced torque reserves, later than with higher levels of the latter. The larger ratio effective after shifting can, in spite of full engine power, lead to negative vehicle acceleration.
Moreover, a jerk-free shifting cannot be ensured since upon a speed change there is no possibility of influencing the timing of the closing and opening of the clutches to be shifted.
If the vehicle is moving down an incline, for which additional engine braking is desired to supplement the mechanical or hydraulic brakes, the momentum can result in an upshifting which further accelerates the vehicle, especially a load-carrying or utility vehicles with a torque converter and a retarder requiring total control to ensure an optimum shifting ratio in the corresponding use ranges of the vehicle for different operating conditions.